Testing Legacy Code effectively with Approval Tests

You've inherited some legacy code: it's valuable, but it doesn't have tests, and it wasn't designed to be testable, so you need to start refactoring. But you can't refactor safely until the code has tests, and you can't add tests without refactoring! How can you ever break out of this loop?

Whether Legacy code for you means "old code", "code without tests", or "code you wish to redesign for new features or unit-tests", this workshop will enable you to become productive and work safely, quickly.

In this hands-on workshop, you will learn not just how to use Approval Tests to start testing legacy code, but how to create effective, maintainable, expressive tests, even on large systems.

Prerequisites

• Some prior experience of programming in C++
• The ability to run AnyDesk and Zoom, with a microphone and video camera.
• We suggest running Zoom on a second device (such as a phone or tablet)
• Optionally, a GitHub user name is helpful, for sharing code

Environment

This entire course is a workshop, with very little "lecturing", and a lot of interactive pair and group working. Our goal for this course is helping you gain Proficiency, and that requires hands-on practice.

For simplicity of setup, we will provide a virtual machine that you will be accessing via AnyDesk. It will be configured with:

• Windows
• CLion
• C++17
• Catch2
• CMake
• Git and GitHub Desktop
• A graphical diffing tool

(What we teach applies is generally applicable to a much wider range of C++ versions, IDEs, test frameworks and build systems than the above.)

Syllabus/Topics

• Testing legacy code
• Testing functional code
• Combination Testing
• Breaking the cycle of can't refactor/no tests
• Breaking up an existing application to add tests
• Approval Tests
  • Write first Approval Test
  • Dealing with non-stable output
  • Using Approval Tests effectively, for highly maintainable tests
• Writing expressive tests